Automated conveyor systems for the assembly of products are well-known. Automated conveyor systems can be divided into two principal categories: synchronous and non-synchronous. The present invention is directed to non-synchronous assembly systems and specifically to the problem encountered when a moving carrier slams into or otherwise is stopped by a stationary or queued carrier located downstream from the moving carrier. The present invention is directed to an improved system that buffers the collision between two carriers thereby reducing shock transmitted to the products disposed on top of the carriers. The present invention further provides a means for preventing forward movement of a queued carrier and eliminating or drastically reducing shock transmission to the queued carrier as it is struck from behind by an oncoming carrier. The present invention may also provide a means for stopping an oncoming carrier as it engages a queued carrier.
Workpieces are transported from stage to stage in an assembly system by carriers or carrier assemblies which ride on top of the conveyor or conveyor chain. In a synchronous assembly system, a workpiece and carrier proceed through each stage of the assembly process and do not proceed to the next stage until the remaining workpieces are also ready to proceed to the next stage (i.e., each workpiece is in synch with the other workpieces). Thus, in synchronous assembly systems, the conveyor stops after each workpiece arrives at its respective processing stage and the stage or task that takes the greatest amount of time will limit the rate at which all other tasks or stages can be completed because the conveyor will not resume a forward motion until all the workpieces, including the workpiece at the slowest stage, are ready to proceed to the next stage.
In contrast, in non-synchronous assembly systems, the conveyor is continuously moving forward. Slower tasks are performed in multiple by employing combinations of divide modules or divide sections. At a divide section, carriers are routed from the main conveyor to spurs so that the slow task may be performed on a number of workpieces on the conveyor system at the same time. Divide sections are designed to send workpieces with the slowest task completed down the conveyor at the line rate or the rate at which the main conveyor chain is moving. After a slower task is completed, the workpiece is returned to the main conveyor chain via a merge module. A slower assembly task may also be performed by physically removing the workpiece and carrier from the conveyor, performing the task, and returning the workpiece and carrier to the conveyor where the workpiece and carriers are transported by the moving conveyor to the next stage. Because the workpieces and carriers are removed from the main conveyor chain either by physical displacement or by splitting workpieces off onto divide sections, the slower tasks to be performed do not become the limiting factor in the throughput of the system.
In buffer/queuing situations, a series of carriers may accumulate at a work station where a task is being performed. As an oncoming carrier arrives, it will slam into or engage a queued carrier that precedes it on the conveying line. To alleviate this situation, a buffer stop may be employed upstream of the work station to relieve the back pressure caused by the oncoming carriers. A queue stop may also be employed to protect the carrier at the work station from being hit or struck by an oncoming carrier because collisions between carriers result in the dissipation of kinetic energy which may dislodge the workpieces disposed on the carriers as well as disrupt the task being performed at the work station.
The carrier that is moving with the conveyor will hereinafter be referred to as the "oncoming" carrier; the carrier that is stopped and is waiting to be received at a work station or queue stop will hereinafter be referred to as a "queued" carrier.
U.S. Pat. No. 4,605,121 discloses the use of a freely disposed buffer ring that is placed on the conveyor between two carriers. One drawback to the system disclosed in the U.S. Pat. No. 4,605,121 is that the freely disposed buffers can often become separated from the carriers if the system includes divide or merge sections and thus their ability to perform their sole and essential task is lost; freely disposed buffers can only work if they are disposed between two carriers. Further, the freely disposed buffers do not carry workpieces and therefore consume space on the conveyor chain that could be utilized to carry workpieces.
Thus, there is a need for an improved carrier that includes built-in shock-absorbing and bumper capabilities to limit the impact on workpieces disposed on the queued carrier when an oncoming carrier forcefully engages it. Further, there is a need for a carrier that includes a built-in braking ability so that when an oncoming carrier engages a queued carrier, the queued carrier will not only absorb shock but will also act to brake itself thereby lessening the effect of the collision on the queued carrier and any other carriers disposed in front of the queued carrier. There is also a need for an improved bumper/braking system for mounting on the front ends of oncoming carriers that will act to brake an oncoming carrier at the point of impact with a queued carrier.